This research will cover several aspects of ovarian regulation during pregnancy. The mechanism of luteinization in the rabbit Graafian follicle will be investigated using a new approach: follicles incubated with hormones or nucleotides which initiate luteinization are immediately auto-transplanted beneath the kidney capsule where they readily luteinize and develop into ectopic corpora lutea. Intraovarian regulation of progesterone synthesis in the corpus luteum by steroids from the interstitial gland (20 alpha-dihydroprogesterone) and from ovarian follicles (17B-estradiol) will be investigated in rabbits. A suspected gonadotropic or luteotropic hormone produced by the rabbit conceptus will be studied for its ability to stimulate follicular estradiol synthesis and to maintain luteal synthesis of progesterone. Finally, efforts will be made to determine whether estradiol can directly stimulate luteinization and progesterone synthesis in rabbit granulosa cells maintained in tissue culture.